Cartilaginous anatomical structures of the human body have a compliancy and malleability that, at least in some of those structures, allow the cartilage to be compressed, displaced, or otherwise temporarily altered in shape, without injury, by the application of an externally-applied object to said cartilaginous structure.
It is opportune that earpieces can be used in the ear canal because of the human tissue materials comprising the outer portion of the ear canal wall (i.e., that which is proximal to the ear canal rim or opening); this tissue being flesh over cartilage for up to about one-half of the total depth of the ear canal (and then being flesh over bone for approximately the inner half of the total depth). As such, most ear canal insert devices will engage at least the cartilaginous region, and may extend into the bony-walled region.
In current practice, an attempt is made to reduce movement of ear inserts, such as hearing aids, and loss of acoustic seal by molding custom-molded ear inserts or hearing aids as slightly oversized (larger) than the ear impression obtained on the user, and this oversizing is generally achieved along the full surface area of the insert. Another current practice technique is to add one or more ring-shaped projections or attachments, such as an O-ring, which encircle the insert around its cross-section. However, while either of these approaches may offer some resistance to the insert moving backward out of the ear, neither prevents the insert from moving in the yaw or roll axes as described above, and neither provides an effective countermeasure against the loss of seal which can readily occur during jaw movements. For example, the ring projection does not help in reducing yaw motions because the ring acts as a pivot point about which the earplug can wobble, and it does not help in roll because it establishes no edge against the ear canal walls in the cross-sectional direction. Furthermore, both the oversized ear impression and the ring approaches may result in pain because the ear canal is essentially “stretched” over a substantial portion of its surface. It is also important to recognize that a uniformly oversized hearing aid engages the compliant, cartilaginous portion of the ear canal in a uniform manner, thus being free to “float” within the ear canal cavity, thereby responding to jaw movement by moving itself, thereby being rendered as physically unstable in the canal and losing its acoustic seal. Furthermore, a common occurrence with a hearing aid wherein a loss of seal is experienced is acoustic feedback between the external microphone and the receiver loudspeaker which the external microphone then acoustically confronts due to the loss of seal that separates the two. This feedback is typically heard as an audible “squeal,” and is objectionable to both the user and others in the vicinity.
In addition to ring projection systems, several related art systems use a trench vent and/or a duct ven, the purpose of which is to form a pathway through which air (and thus sound) can pass, being advantageous for improving the acoustic response of the hearing device, and for reducing the objectionable “occlusion” effect which manifests as the user's voice sounding bassy and resonant to himself or herself.